This invention relates to electromechanical transducer-coupled vibrating mechanical structures, and more particularly, it relates to an arrangement for compensating for the inherent transducer capacitance of such structures.
A significant source of error in high precision mechanical and electromechanical structures is vibration. Antennas, optical structures, pointing and tracking systems, seeker heads, gravitational and inertial sensors, and guidance platforms can suffer a degradation in performance from external excitation by the local acoustic and vibrational environment.
In the past, the effects of externally induced vibrations in large mechanical structures have been mitigated by such brute-force techniques as stiffening the structure, adding massive mechanical dampers, covering the structure with viscoelastic damping material, or adding acoustic shielding and vibration isolators to shield the structure from the environment.
A further approach to mitigating the aforementioned vibration effects involves electronically damping or controlling the vibrations. In order to accomplish this, an electromechanical transducer, such as a piezoelectric strain transducer, is mounted on the vibrating mechanical structure to provide an electrical signal responsive to the vibrational motion of the structure. This electrical signal may be either applied to a damping resistor connected across the transducer output terminals or fed to electronic processing circuitry for developing an appropriate control signal which is fed back to the mechanical structure via a further electromechanical transducer. Regardless of the particular approach employed, the inherent capacitance of the signal-extracting electromechanical transducer significantly limits the degree of coupling to the external electronic circuitry. This, in turn, limits the degree of electronic damping or control which may be achieved.
In my co-pending application entitled "Passive Vibration Damping System--Active Vibration Damping System", Ser. No. 901,550, filed May 1, 1978, an arrangement is disclosed for tuning out the inherent shunt capacitance of the transducer by connecting across the transducer output an inductor which provides the appropriate inductance to resonate with the transducer inherent capacitance. Such an arrangement is highly effective in eliminating the effect of the transducer capacitance at vibration frequencies in the vicinity of the inductance-capacitance resonant frequency, although its effectiveness is reduced as the vibration frequency departs from the resonant frequency.